JSDocThisTag with no type expression has empty type expresison node

[dsherret]

TypeScript Version: 3.8.0-dev.20200208

Search Terms: JSDocThisTag typeExpression

Code

const sourceFile = ts.createSourceFile("test.ts", `/**
 * @this - Some description.
 */
function test() {}`);

console.log(sourceFile.statements[0].jsDoc[0].tags[0].typeExpression);

Expected behavior: Undefined as type declaration has that as a possibility.

Actual behavior: { pos: 13, end: 13, ... }

Select Options -> typescript@next and check "Show internals":

https://ts-ast-viewer.com/#code/PQKhCgAIUgBAXAFgSwM6QLSQMoHsC2AppACaGoDGATsgA7zK4B2AdFCMOAGYCuTFDZpHjl4ACgCUkAN4BfIA

[sandersn]

As far as I can tell, tags that error on a missing type create an empty type expression. Tags that don't have the property undefined.

Returns an empty type expression:

• @enum
• @this
• @type

Returns undefined:

• @param
• @return

The problem is that typeExpression is marked optional on JSDocEnumTag and JSDocThisTag, and they shouldn't be.